Initial Surfactant Concentration Research Articles

The effect of surfactants on the instability of a rotating liquid jet

It has long been known that the presence of surfactants on the free surface of a liquid jet can create surface tension gradients along the interface. The resulting formation of tangential stresses along the surface lead to Marangoni type flows and greatly affect the resulting dynamics of rupture. In this way surfactants can be used to manipulate the breakup of a liquid jet and control the size of droplets produced. In this paper we investigate the effects of insoluble surfactants on the breakup of rotating liquid jets with applications to industrial prilling. Using a long wavelength approximation we reduce the governing equations into a set of one-dimensional equations. We use an asymptotic theory to find steady solutions and then carry out a linear instability analysis on these solutions. We show that steady state centreline solutions are independent of viscosity to leading order and that the most unstable wavenumber and growth rate of disturbances decrease as the effectiveness of surfactants is increased. We also numerically solve these equations using a finite difference scheme to investigate the effects of changing the initial surfactant concentration and other fluid parameters. Our results show that differences in breakup lengths between rotating surfactant-laden jets and surfactant-free jets increase with the rate of rotation. Moreover, we find that satellite droplet sizes decrease as the rate of rotation is decreased with the effect of surfactants amplifying the reduction in sizes. Furthermore, the presence of surfactants at fixed rotation rates is shown to produce larger main droplets at low disturbance wavenumbers whilst satellite droplets are smaller for moderate disturbance wavenumbers κ ≈ 0.7 .

CONTROLLED-RELEASE PREDNISOLONE POLY (DL-LACTIDE) MICROSPHERES: IMPACT OF FORMULATION PARAMETERS, CHARACTERIZATION AND RELEASE MECHANISM

The steroidal drug prednisolone was encapsulated into microspheres using the biodegradable polymer poly (DL-lactide) using emulsion-solvent evaporation method. The produced microspheres were characterized using scanning electron microscopy, X-ray diffractometery, FT-IR spectroscopy, DSC, and laser light diffraction. The morphology, particle size distribution, encapsulation efficiency (EE%), and drug release showed marked dependence upon formulation parameters viz. initial polymer concentration, surfactant concentration, drug-to-polymer ratio, and volume of the external aqueous phase. The effect of the addition of hydrophilic additives such as PVP or PEG 8000 was also investigated. The encapsulation efficiency percent and the mean particle size were increased by increasing the initial polymer concentration and drug polymer ratio. On the other hand, increasing the surfactant concentration resulted in decreasing the mean particle size and increasing the drug release from the microspheres. The probable mechanism of drug release was estimated and found to be via diffusion through channels and/or pores present within the polymeric matrix. Release data of almost all formulae fitted Higuchi's planar model better than spherical model. This finding could be due to the small extent of drug release (~ 40%), or the presence of a large fraction of the encapsulated drug nearby the surface of the microspheres.

Effect of nonionic surfactants on biodegradation of phenanthrene by a marine bacteria of Neptunomonas naphthovorans

Biodegradation of three nonionic surfactants, Tergitol 15-S- X ( X = 7, 9 and 12), and their effects on the biodegradation of phenanthrene by marine bacteria, Neptunomonas naphthovorans, were studied. The experimental outcomes could be fit well with the first-order biodegradation kinetics model. It was observed that the biodegradability of these surfactants decreased with an increase in the chain length of the hydrophilic moiety of the surfactant. When surfactant concentrations initially present were less than 250 mg carbon/L, biodegradability of Tergitol 15-S- X surfactants is around 0.3. Reduced biodegradability of Tergitol 15-S-7 and Tergitol 15-S-9 was observed when their concentrations initially present were increased to 322 and 371 mg carbon/L, respectively. In general, biodegradation of phenanthrene was enhanced with increasing solubilization of phenanthrene by these surfactants. However, with the same initial concentration of phenanthrene, biodegradability of phenanthrene was found to decrease with an increase in surfactant concentration. For these three surfactants, more than 80% of the phenanthrene was degraded when surfactant concentrations initially present were 200 mg/L. However, less than 30% of phenanthrene could be degraded, if initial surfactant concentrations were increased to 1000 mg/L. Interestingly, the concurrent biodegradation of the surfactants reduced their effective concentrations for micelle formation and, hence, contribute to the higher bioavailability of phenanthrene by gradually releasing phenanthrene molecules into the aqueous phase.

The photodegradation of trichloroethylene with or without the NAPL by UV irradiation in surfactant solutions

The photodegradation of trichloroethene (TCE) with or without nonaqueous phase liquids (NAPL) by ultraviolet irradiation in surfactant solutions was examined in this study. The photodecay of TCE was studied at monochromatic 254 nm UV lamps. The effects of the type of surfactants, initial surfactant concentrations, pH levels and NAPL concentrations were examined to explore the photodecay of TCE. All the photodegradation of TCE followed pseudo-first-order decay kinetics at various conditions. It was found that Brij 35 overdose and higher initial pH levels may retard or inhibit the photodecay of TCE, mainly due to protons, intermediate generation and change of surfactant structure in the processes. The optimal condition for TCE photodecay was suggested based on the analysis of kinetics data, from which the reaction mechanism of TCE in the presence of NAPL form was also studied. In general, the reactions of TCE in micellar solution and NAPL pool can be considered as independent pathways due to the low molecule diffusion between the two phases.

Diclofenac sodium loaded-cellulose acetate butyrate: Effect of processing variables on microparticles properties, drug release kinetics and ulcerogenic activity

The aim of this study was to develop and characterize diclofenac sodium loaded-cellulose acetate butyrate microparticles in order to obtain a controlled-release system. The influence of the type of polymer, the volume and composition of the internal phase, drug loading, surfactant concentration and additive added on microparticles characteristics (particle size, encapsulation efficiency, surface morphology and in vitro release profiles) was studied to optimize the microparticles system. The resultant microparticles were evaluated for the recovery, average particle size, drug loading and incorporation efficiency. The microparticles exhibited good flowing nature and compressibility index when compared to pure drug. Dissolution rate of diclofenac sodium in phosphate buffer (pH 6.8) increased with increases in initial drug loading, surfactant concentration and addition of alcohol as co-solvent but decreased with increases in the concentration of additives such as Gantrez® AN or Eudragit S100 in the internal phase. The dissolution data showed a Higuchi diffusion pattern for most of the formulations. About 56–81% reduction in ulcerogenic activity was observed with microparticles containing Eudragit S100 17–25%, based on total polymer concentration, when compared with pure diclofenac sodium.

X‐ray Diffraction Study of the Structure of Carboxymethylcellulose–Cationic Surfactant Complexes

We have investigated dilute aqueous solutions of an anionic polymer (carboxymethylcellulose) mixed with cationic surfactants of different chain lengths (dodecyl to octadecyl trimethylammonium bromides: DTAB, TTAB, CTAB and OTAB). The structures of the concentrated phases formed above the precipitation threshold were studied by X-ray diffraction. Different body-centred cubic structures with space groups Pm3n were observed in the presence of surfactant with a short aliphatic chain (DTAB), despite the fact that the polymer persistence length is comparable to the repeat distance of the structure (5 nm). For larger surfactant chain lengths (TTAB and CTAB), the structure of the precipitates can be either cubic (Pm3n) or 2D hexagonal depending on the initial surfactant and polymer concentrations. For still larger chain length (OTAB), the structure becomes lamellar. This structural evolution from micellar cubic towards 2D hexagonal and lamellar is attributed to the decrease of the local curvature of the surfactant aggregates, as observed for flexible synthetic polymers and short DNA fragments under similar conditions. Furthermore, the structure of the bulk complexes formed just below the precipitation threshold anticipates the structure seen in the precipitated phases.

Sorption of synthetic surfactants by “Policon” materials

The effect of the initial concentration of synthetic surfactant (SSF) in wastewaters on sorption was investigated, and Policon materials were recommended for use in the tertiary treatment stage where the concentration of SSF does not exceed 0.8 mg/dm3. It was noted that increasing the temperature of the effluents by 60° allows significantly extending the period of steady-state flow of the process and the depth of treatment remains high. The selectivity of Policon materials with respect to the SSF contained in synthetic detergents was investigated. The high efficiency of the materials in ultrafiltration of the components of synthetic detergents was demonstrated.

Synthesis, aggregation and photoinduced electron transfer processes of cationic water-soluble 21-thia and 21-oxaporphyrins

The meso-pyridyl 21-thia- and 21-oxaporphyrins containing three pyridyl groups at the meso-positions have been methylated to obtain water-soluble porphyrins. The porphyrins are highly soluble in water and the water-soluble 21-thiaporphyrins exhibit aggregation behaviour above 10 −4 M whereas the water-soluble 21-oxaporphyrins strongly aggregate at very low concentrations (10 −7 M). The interaction of water-soluble ionic porphyrins with ionic surfactant in aqueous solutions has been studied as a function of surfactant concentration by means of absorption, fluorescence and resonance light scattering (RLS) techniques. It has been observed that, at the initial premicellar surfactant concentration, the oppositely charged surfactant induces aggregation and above cmc these aggregates dissociates into monomeric form and gets micellised. The self- and SDS-induced aggregation of these cationic porphyrins is found to depend on the number and position of the positive charge with respect to the porphyrin core. The micellar encapsulation technique is used to promote the photoinduced electron transfer between the porphyrins and neutral aromatic amines and it has been observed that the electron transfer rate becomes slowing down at the micellar surface compared to the bulk acetonitrile solution.

Cloud-point extraction of selected polycyclic aromatic hydrocarbons by nonionic surfactants

Effect of nonionic surfactants on the performance of the cloud-point extraction (CPE) processes in preconcentrating trace amount of polycyclic aromatic hydrocarbons (PAHs), consisting of two to five fused rings, from aqueous solution at 25 °C was studied. Three biodegradable nonionic surfactants with molecular similarity were employed. Cloud-point temperatures (CPTs) of these micellar solutions were regulated and reduced enough with addition of sodium sulfate and sodium phosphate, so that the CPE process could be facilitated at 25 °C. Furthermore, quadratic equations in additive concentration are found to fit the CPTs of these micellar solutions well. It is observed that the preconcentration factor could be enhanced either by increasing the salt concentration or by decreasing the initial surfactant concentration present in the micellar solution. With CPTs regulated at around 15 and 18 °C with addition of Na 2SO 4 and Na 3PO 4, preconcentration factors in between 30 and 45 obtained from 1 wt% micellar solutions of these three surfactants appear in the order of Tergitol 15-S-9 > Neodol 25-7 > Tergitol 15-S-7, coincidently with the hydrophilicity order of surfactants. The average preconcentration factor was empirically fitted well as a simple power-law function of surfactant concentration used in the CPE process. The obtained empirical power-law indices are close to negative unity.

Concentrated Bitumen-in-Water Emulsification in Coaxial Mixers

A semibatch bitumen emulsification process to generate droplet size in the submicrometer range was developed in a coaxial mixer using a high-internal-phase ratio (HIPR) step followed by dilution to the final concentration of the dispersed phase. An HIPR emulsion is characterized by nonspherical droplets shape separated by thin films due to low ratio between the continuous- and dispersed-phase concentrations. The same mixing system was used to prepare the HIPR intermediate and the eventual emulsion, based on a pitched blade turbine on the high-speed shaft and two different types of close-clearance impellers on the low-speed shaft. It was found that the most critical process stage to achieve the mean droplet size was the preparation of the HIPR emulsion. The dispersed-phase and surfactant concentrations, the close-clearance impeller rotational speed, and agitation time were identified as key process parameters to control the droplet size. These parameters were combined to provide a prediction model of the average droplet size with two dimensionless parameters, namely, the initial surfactant concentration in the continuous phase and the bitumen weighted deformation.

Dynamic Performance of Ozonation Treatment for Nonionic Surfactants (Polyoxyethylene Alkyl Ether) in a Bubble Column Reactor

The ozonation of a nonionic surfactant, Sannonic SS-90 (polyoxyethylene alkyl ether), which is one of polyoxyethylene nonionic surfactants, in water has been investigated using a bubble column. The effects of initial nonionic surfactant concentration, ozone gas flow rate, inlet ozone concentration in the gas-phase, liquid-phase temperature and hydrogen peroxide dose on decomposition of Sannonic SS-90 were systematically examined. The decomposition rate of Sannonic SS-90 decreased with the increase in the initial surfactant concentration and increased with increasing ozone flow rate and temperature. It was found that the rate of Sannonic SS-90 mineralization was weakly dependent on the gas-phase inlet ozone concentration in the range of the gas-phase inlet ozone concentration in this study. The oxidation rate increased with increasing concentration of H2O2, reached a maximum value and then decreased with further increasing of H2O2 concentration. The dynamic performance of the ozonation in a semi-batch bubble column was simulated using a mathematical model based on a tanks-in-series model. Reasonable agreement between the present experimental data and the simulated results was found.

Convective self-oscillations near an air-bubble surface in a horizontal rectangular channel

The concentration convection in an isothermal fluid near an air bubble clamped between the vertical walls of a horizontal channel with a rectangular cross-section is studied experimentally and numerically. The channel is filled with an aqueous solution of a surfactant with a nonuniform concentration. As a result of the competition between the gravitational convection in the cavity volume and the Marangoni convection near the bubble surface, an oscillation flow regime is established. This regime is observed experimentally over several hours. In the numerical experiment, the oscillations are obtained in the presence of an initial horizontal surfactant concentration gradient. Against the background of gravitational convection, short bursts of Marangoni convection with ten times greater intensity are observed. The convective flow patterns and the oscillation periods obtained experimentally and numerically are in fairly good agreement.

Kinetics and isotherms of adsorption of alkyldimethylamine oxide on a porous hydrophobic polymer: A thermodynamic approach to a Langmuir-like phenomenon

We studied the adsorption of decyl-, dodecyl- and tetradecyldimethylamine oxide surfactants on porous beads of polystyrene divinylbenzene (Bio-beads SM2). The concentration of free surfactant is followed in situ using an ion-selective electrode. Isotherms for the three surfactants were determined using a batch method at 25 °C. We tested various parameters for their influence on the adsorption kinetics: initial surfactant concentration (below and above the critical micellar concentration (CMC)), initial quantity of bead, temperature and surfactant chain length. The behaviour can be modelled using a generalised Langmuir kinetics approach that assumes systems do not possess adsorption sites. We used the same set of parameters for the isotherm and kinetics results. These parameters are linked to the parameters from the Langmuir equation and we discuss the validity of the model. Although the proposed model does not require any adsorption sites, the results from the model are similar to the Langmuir approach. Adsorption is shown to be due to hydrophobic interactions.

Removal of Aluminum from Some Water Samples by Sorptive-Flotation Using Powdered Modified Activated Carbon as a Sorbent and Oleic Acid as a Surfactant

Bench-scale experiments were conducted in the laboratory, aiming to remove aluminum from water. They were based on using powdered activated carbon (PAC), which was prepared from olive stones generated as plant wastes and modified with an aqueous oxidizing agent as HNO3 as an effective sorbent and oleic acid (HOL) as a surfactant. The main parameters (namely: initial solution pHs, sorbent, surfactant and aluminum concentrations, shaking time, ionic strength and the presence of foreign ions) that influence the sorptive-flotation process were examined. Good results were obtained under the optimum conditions, according to which nearly 100% of aluminum, at pH 7 and at room temperature (approximately 25 degrees C), was removed. The procedure was successfully applied to recover aluminum spiked to some natural water samples. Moreover, a sorption and flotation mechanism is suggested.

Effect of temperature on the biodegradation of linear alkylbenzene sulfonate and alcohol ethoxylate

AbstractThe effect of temperature on the biodegradation of linear alkylbenzene sulfonate (LAS) and alcohol ethoxylate (AE) was evaluated using method OECD 303 A, Confirmatory test (Husmann units). The experiments were performed using an initial surfactant concentration of 10 mg/L and working temperatures of 25, 15, and 9°C, keeping the biodegradation units inside a thermostatic chamber. In all cases, the removal of both surfactants tested, LAS and AE, was higher than 90%, regardless of the temperature used in the test. We observed that longer acclimation periods were needed by the microorganisms at lower temperatures.

Styrene Emulsion Polymerization above the CMC: New Evidence on Particle Nucleation by means of AFFFF

AbstractSummary: The number (N) and size distribution of particles (PSD) of a styrene emulsion polymerization above the CMC were studied by means of asymmetric flow‐field flow fractionation (AF4). Bimodal PSDs were obtained, suggesting that coagulation of the primary particles is not as extensive as would be expected, according to the coagulative mechanism. AF4 allowed it to be demonstrated that N is constant during interval II, and that the resolution limit of other particle sizing techniques can lead to erroneous mechanistic inferences, from the evolution of N.Particle size distribution measured at low conversion for the emulsion polymerization of styrene, obtained by AF4 and DLS. The initial surfactant (S0), initiator (I0) and monomer (M0) concentrations are indicated in the figure.magnified imageParticle size distribution measured at low conversion for the emulsion polymerization of styrene, obtained by AF4 and DLS. The initial surfactant (S0), initiator (I0) and monomer (M0) concentrations are indicated in the figure.

RETRACTED: Solubilization of DNAPLs by mixed surfactant: Synergism and solubilization capacity

Efforts to remove the dense nonaqueous phase liquids (DNAPLs) in subsurface by mobilizing them face with risks of driving the contaminants deeper into aquifer zones. In this paper, a synergistical solubilization of DNAPLs by mixed nonionic and anionic surfactant, Triton X-100 (TX100) and sodium dodecylbenzene sulfonate (SDBS) in DNAPL/water systems was presented. Given 1:40 phase ratio of DNAPL:water (v/v), mixed TX100-SDBS exhibited significantly synergistical solubilization for the DNAPLs, trichloroethene (TCE), chlorobenzene (CB) and 1,2-dichlorobenzene (1,2-DCB), respectively, when the total surfactant concentration was up to 6000mg/L, i.e. the condition when solubilization by the mixture was better than those attainable with individual components by themselves. The synergistical extents depended on the initial ratios of TX100 to SDBS, the initial surfactant concentrations and the properties of DNAPLs. Given the total surfactant concentration, synergistical extents increased with the fraction of SDBS in mixed surfactant. On the contrary, did with the total surfactant concentration. The solubilization capacity by 3:1, 1:1 and 1:3 of mass ratio of TX100-SDBS were determined and compared with those by single ones. In the view of the mass solubilization ratio (SR), the mixed TX100-SDBS could solubilize more DNAPLs than single SDBS at given surfactant concentration. Reduction in partition of TX100 and synergistic solubilization were responsible for the significant solubilization extent of mixed system. The work presented here demonstrates that mixed nonionic-anionic surfactants would be preferred over the corresponding single surfactants for solubilization remediation of DNAPLs, which could decrease risks of driving the contaminants deeper into aquifers.

Mixed Solutions of an Associating Polymer with a Cleavable Surfactant

Mixtures of hydrophobically modified hydroxyethyl cellulose (HMHEC) and alkali-sensitive cleavable betaine ester surfactants have been studied by viscometry, 1H NMR, absorbance measurements, and birefringence determinations. Before the hydrolysis, the surfactants behaved as conventional nondegradable surfactants in terms of the effect on the viscosity of increasing surfactant concentration. As the surfactants were hydrolyzed, systems with time-dependent viscosity were obtained. The viscosity either decreased monotonically or went through a maximum as a function of time, depending on the initial surfactant concentration. Different surfactant chain lengths gave rise to different viscosity profiles. The rate of hydrolysis, and thus the time-dependency of the surfactant concentration, could be controlled by changing the pH of the solution.

Thermal Characterization of Surfactant-Modified Montmorillonites

AbstractThe thermal stability of surfactant-modified clays plays a key role in the synthesis and processing of organoclay-based nanocomposites. Differential thermal analysis (DTA), thermogravimetric measurement and differential scanning calorimetry (DSC) were used in this study to characterize the thermal stability of hexadecyltrimethylammonium bromide-modified montmorillonites prepared at different surfactant concentrations. Analysis by DSC shows that the molecular environment of the surfactant within the montmorillonite galleries is different from that in the bulk state. The endothermic peak at 70–100°C in the DTA curves of the modified montmorillonites is attributed to both the surfactant phase transformation and the loss of free and interlayer water. With an increase of surfactant-packing density, the amount of water residing in the modified montmorillonite decreases gradually, reflecting the improvement of the hydrophobic property for the organoclay. However, the increase in the surfactant packing density within the galleries leads to a decrease in the thermal stability of the organoclays.With an increase of initial surfactant concentration for the preparation of organoclays, the surfactant- packing density increases gradually to a ‘saturated’ state. It was found that the cationic surfactant was introduced into the montmorillonite interlayer not only by cation exchange but also by physical adsorption.

Solubilization of Phenols in Anionic Polyelectrolyte Gels with Adsorbed Cationic Surfactant

Solubilization isotherms for various phenols in cetylpyridinium chloride (CPC)-polyelectrolyte gel aggregates have been determined in order to compare solubilization within these aggregates with that in free micelles and to examine the effects of gel chemistry and structure on solubilization. The isotherms describing solubilization are quite similar to those found for free surfactant in solution. Solutes that are more hydrophobic give rise to larger solubilization constants with trends similar to what is seen for hydrophobic effects in adsorption from aqueous solutions onto hydrophobic solids. The solubilization constants decrease as the fraction of solute in the aggregates increases, indicating that the solutes partition into the palisade region of the aggregates. Solubilization is found to be quite insensitive to changes in gel structure (cross-linker varying from 1% to 3%) and chemistry (poly(acrylic acid) versus poly(methacrylic acid) and neutralization from 50% to 100%). However, the switch from poly(acrylic acid) to poly(methacrylic acid) did give rise to a slight decrease in magnitude of the slope of the isotherm. The most significant factors appear to be the initial concentration of surfactant in solution and the ratio of surfactant solution to gel amount. A decrease in surfactant concentration (especially combined with an increase in solution volume) gives rise to a decrease in solubilization constants.